In robot-controlled production, there is usually a high demand for precision in the delivery of raw material. For example, when feeding fiber thread to a robot-controlled fiber feeding apparatus, the feeding rate may be about 10 meters per second. If jerks occur in feeding, the thread may be torn off or damaged, which will lead to serious losses in production.
When cutting fiber thread, a cutting apparatus of the above described type is normally used. Each time the fiber thread is hit by the sharp edge of the knife means, the fiber is folded in V-shape around the edge while being pressed into the elastic layer of the support roller. This operation occurs at a high frequency during a period of time of some fractions of a second. The mechanical deformation leads to fracture of the single fibers of the thread.
Known apparatus for this purpose are adapted to cutting fibers of a certain thread length. The distance between two cuts normally depends upon the distance between the knife means of the cutter. Thus, the feeding rate of the feeding rollers and the cutter is synchronized.
It would be desirable to be able to vary the length of the cut fiber pieces inf initely variable. Besides, a drawback with the method is in that a sudden jerk is developed in the thread each time it is hit by a knife means, because the thread is momentarily accelerated while being folded around the knife edge. These rapid jerks can lead to tearing off of the fiber thread at wrong places.